A brief writeup of an interview, with Steve Jobs on the New York Times website, stated;

In contrast, Mr. Jobs said that multitouch drastically simplified the process of controlling a computer.

There are no “verbs” in the iPhone interface, he said, alluding to the way a standard mouse or stylus system works. In those systems, users select an object, like a photo, and then separately select an action, or “verb,” to do something to it.

The Apple development team worried constantly that the approach might fail during the years they were creating the iPhone, he said.

This is easily noticeable when you use the iPhone, everything seems much more ‘complex’ and ‘fussy’ on the desktop after you’ve used it for hours on end. For example, I started to scroll the wrong way when I came back to my Macbook Pro (something I heard more people have had); everything in the iPhone interface feels like it’s how a ‘physical object’ would react. This only proves how far Apple has went to establish a new, even more user-friendly interface paradigm where they went as far as to challenge existing conventions .